The present invention relates to a thermoelectric cooling system based on the Peltier effect, for reducing heat of a transistor provided in a circuit.
The principle of the Peltier effect is a phenomenon that if a direct current is passing through two dissimilar metals such as conductor and semiconductor which are in contact with each other, absorption or radiation of heat other than the Joule heat occurs at a junction. For example, if the direct current flows from a metal to a P-type semiconductor, heat is absorbed at a junction. If the current flows in the reverse direction, heat is radiated at the junction. If the direct current flows from a metal to an N-type semiconductor, heat is radiated at a junction. If the current flows in the reverse direction, the heat is absorbed at the junction.
The thermoelectric cooling device has various superior characteristics. For example, since no movable portion is provided, noises do not occur. Furthermore, in the device using the thermoelectric cooling device, temperature is easily adjusted, the device can be used as a cooling device or a heating device only by changing the direction of flow of the current, and the size of the device is reduced. Thus, the cooling device has been practically used for a small refrigerator, isothermal bath, dew point thermometer, electronic device, and others.
Japanese Patent Application Laid-open 63-6864 discloses a thermoelectric cooling system where a transistor is provided with a P-type semiconductor disposed between metal plates. A current for cooling the transistor is applied from a dependent supply source to the transistor through an input/output lead and fed to a heat sink through the P-type semiconductor. The cooling current is set to a constant value. The heat is absorbed at a junction of one of the metals adjacent to the transistor and the P-type semiconductor. The heat is radiated at a junction of the other metal adjacent to the heat sink and the P-type semiconductor. The heat is discharged from the heat sink to the atmosphere.
In the cooling system, if a driving current of the transistor changes in accordance with driving conditions of the transistor, the amount of heat of the transistor changes. Since the current is constant regardless of the change of the driving current, cooling dependent on the change of the driving current is not effected. Therefore, if the transistor is driven at a low load, the power for cooling current is wasted. Furthermore, the transistor may be over-cooled. In such a case, an operating point of the transistor may be deflected to distort a signal waveform.